1. Field of the Invention
This invention relates to vehicle lifts.
2. The Prior Art
Vehicle lifts for lifting automotive vehicles, such as passenger cars, trucks and buses have been in common use for many years. The lifts for passenger cars and light trucks are usually semihydraulic. Where the lift is to lift trucks and buses, the lift is usually full hydraulic. In all such lifts, a casing for oil of a relatively large diameter and long enough to accommodate the lift to lift the vehicle to the required height forms a guide for a vertically movable plunger which carries a superstructure at its upper end for supporting and lifting an automotive vehicle for servicing. The casing is closed at its lower end by a bulkhead buried in the ground.
In many prior art systems, the cylinder base is buried in concrete for corrosion protection. The balance of the casing is buried in the ground, and may be surrounded by sand to reduce the liability of electrolysis and corrosion. In certain types of soils, however, the sand does not stop electrolysis or corrosion of the casing, resulting in leakage of oil from the casing due to corrosion of the casing and making it necessary to excavate around the casing and remove and replace the casing. This may occur in a relatively short time interval compared to the anticipated life of the casing and results in a time-consuming and expensive operation. This occurs even where the metallic casing is wrapped by fiberglas.
Due to the frequency of leaks caused by electrolysis or corrosion, which is entirely dependent upon the soil and is difficult to predict in advance, the manufacturer of lifts seldom extends its guarantee to the casing.